1. Field of the Invention
The present invention relates to an engine in which a tensioner arm is provided in such a manner as to be in sliding-contact with a cam chain adapted to speed-reduce the rotational power of a crankshaft by half and transmit the resultant power to camshafts for driving an intake valve and an exhaust valve. A screw type lifter having a lifter rod with one end in contact with the tensioner arm is provided in a cylinder head. In particular, the present invention relates to an improved passage structure for feeding oil to a screw type lifter.
2. Description of Background Art
Japanese Patent Laid-open No. Hei 10-238327 discloses an engine, in which oil is generally fed to a screw type lifter through an oil passage branched from a mid point of a passage, which allows oil from an oil pump to flow around a cylinder head. This passage structure; however, has a problem in that the pressure of the oil fed to the cylinder head may be reduced. Specifically, since part of oil to be fed to the cylinder head is branched to the screw type lifter, it may be difficult maintain sufficient lubricating performance required for portions to be lubricated around the camshafts, which are rotated at high speeds. To solve such a problem, it may be considered to increase the discharged pressure of the oil pump; however, in this case, the oil pump must be enlarged. This requires additional installation space for the oil pump, resulting in enlargement of the engine.